The present invention relates to a torus-type apparatus for nuclear fusion. More specifically, the invention relates to a toroidal coil apparatus in which a plurality of coils are arranged in the torus form, and particularly to such a construction for supporting an electromagnetic force.
Generally, the torus-type nuclear fusion apparatus consists, as shown in FIGS. 1 and 2, of a plurality of toroidal coils 1, a vacuum container 2, air-core current transformer coils 3, and poloidal coils 4. The vacuum container 2 has a trapezoidal shape or a circular doughnut shape along the cross section therefore, and a plasma P is confined therein by a magnetic field in the toroidal direction, poloidal direction and vertical direction. The toroidal coils 1 which together surround a vertical center axis and which each surround a a common closed loop axis, have a circular shape or a D-shape to approximate the shape of the plasma P which is heated by an electric current produced by a voltage induced in the plasma P by changing the magnetic flux of the air-core current transformer coils 3 wound in the vicinity of the vacuum container 2.
In a toroidal magnetic field generator of the torus-type nuclear fusion apparatus, in general, heavy currents are permitted to flow in the same direction through a plurality of coils arranged on a torus circle, thereby to generate a toroidal magnetic field. An intense electromagnetic force is generated in the toroidal coils owing to the interaction between the magnetic field and coil currents. The electromagnetic force works as an expanding force F to expand the coils in general, and is so distributed as to become intense toward the inner side of the torus and weak toward the outer side of the torus. Therefore, there develops a force (centripetal force) Fr which acts to collect the plurality of toroidal coils to the center as a whole. Further, heavy currents are permitted to flow into the poloidal coils installed adjacent to the toroidal coils to generate a poloidal magnetic field, thereby to heat the plasma, and to control the shape and the position of the plasma. Here, the poloidal magnetic field intersects the electric currents flowing through the toroidal coils, whereby a force is generated to invert the toroidal coils outwardly at the surface thereof. In the torus-type nuclear fusion apparatus, a problem remains with regard to how to support the electromagnetic force generated in the toroidal coils and how to minimize the stress generated in the toroidal coils.
To cope with this problem, the conventional apparatus has been constructed as shown in FIGS. 3 to 5.
That is, as shown in FIGS. 3 and 4, the toroidal coils 1, each consisting of a conductor wound in a number of turns, are contained in coil support frames 5a, 5b made of a nonmagnetic material such as SUS or a strong aluminum alloy capable of withstanding an intense electromagnetic force generated in the toroidal coils 1. The coil support frames 5a, 5b are strongly fastened at their upper and lower portions to a rack 7 by bolts 8 via coil support legs 6, so as to be capable of withstanding the weights of the toroidal coils 1, heat, electromagnetic force F, centripetal force Fr, and inverting force F.sub.Q. Further, wedge-like coupling portions 5c are provided to support the centripetal force Fr at positions of wedge portions 1a at the inner end portions of toroidal coils 1.
The toroidal coils 1 contained in the coil support frames 5a, 5b are arranged in a plurality of coils in a toroidal direction. Then, a force is applied to the back side of the coils using hydraulic jacks or the like with the coil support frames 5b being located on the center side, in order to collect the toroidal coils 1 in a precise radial form. Then, the coil support legs 6 are fastened and secured to the rack 7 by bolts 8 so that the wedge surfaces of the wedge-like coupling portions 5c provided on the inner side of the coil support frames 5a, 5b are intimately contacted with each other, and that the centripetal force Fr is correctly received via the wedge surfaces. Further, the inverting force F.sub.Q illustrated in FIG. 6 is received by inversion preventing beams 9a, 9b which are provided between the coil support frames 5a and 5b as shown in FIG. 5. In recent years, however, an increase in the scale of the apparatus has resulted in an increased intensity of the magnetic field and increased electromagnetic forces, making it difficult to support the centripetal force Fr and the inverting force F.sub.Q. That is, efforts have been made to maintain the wedge effect against the centripetal force Fr by relying upon the wedge surfaces of the wedge-like coupling portions 5c. However, as the coils are constructed in larger sizes and the total height of the coils becomes large, it becomes difficult to maintain precision while constructing the coils. Therefore, despite the fact that the coils are pushed by hydraulic jacks and are secured by bolts 8, the pushing force Ft for the coils is effective only in the vicinities of coil support legs 6; i.e., it is no longer possible to maintain the pushing force Ft for the total height of the coils. In order to reduce the inverting force F.sub.Q, furthermore, inversion preventing beams 9a, 9b are provided but avoiding the plasma observation ports 10. Therefore, the inverting force F.sub.Q is not supported by the whole surfaces of coils. Further, the distance l increased between the wedge-like coupling portions 5c and the inversion preventing beams 9a, and increased stress is exerted on the straight portions of the coils. Moreover, wedge surfaces of the wedge-like coupling portions 5c are not capable of supporting the pushing force Ft, and hence exhibit rigidity no more against the inverting force F.sub.Q. Furthermore, even if it is attempted to install inversion preventing beams near the wedge surfaces, only very thin inversion preventing beams are allowed to be installed as a result of an increased number of toroidal coils in the apparatuses constructed in recent years. Namely, this arrangement does not permit structure to be employed very thin inversion preventing beams to the coil support frames 5a by coils. It is therefore difficult to reduce stress exerted on the straight portions of the coils.